Distance measuring devices as such have been known for some time. Said devices emit a modulated measuring beam, e.g., a light beam or an ultrasonic beam, that is directed toward a desired target object or a target surface to determine the distance between which said target and the device. Part of the measuring signal that is reflected or scattered, returned by the located target surface is detected again by the device, and it is used to determine the searched-for distance.
The range of application of distance measuring devices of this type generally covers distances in the range of a few centimeters to many hundred meters. Measuring devices of this type are now sold commercially in compact configurations and enable simple, hand-held operation by the user. Moreover, the devices can also be equipped with tripods or holding elements sold as accessories, for example, or they can be equipped for a static measuring process, which is particularly advantageous for taking very exact measurements or measuring very long distances to target objects.
To determine very short distances in particular, it is necessary to assign an unequivocal reference point or reference plane to the measuring device, which said reference point or reference plane being used as the starting point for calculating the distance from the measuring device to the desired target object. With known distance measuring devices found on the market, this reference point is located, e.g., in a housing edge extending at a right angle to the beam direction, such as in the front side of the housing or in the back end of the housing. The user must make certain that the measuring device is positioned during the measuring process such that the reference point or the reference plane of the measuring device intersects exactly with the zero point of the path it will measure.
An opto-electronic hand-held measuring device for measuring distance is made known in WO 94/27164 and in the “Disto” operating instructions from Leica Geosystems AG, 9435 Heerbrugg, Switzerland, 1994. Distances to an object can be measured optically with said device. The distance to the object can be measured starting at either an anterior or posterior measurement stop of the distance measuring device. The front and back housing surfaces of the distance measuring device—which are configured at a right angle to the direction of measurement—generally serve as measurement stops (reference points of the device). A separate measurement button on the keypad of the measuring device is assigned to each of the possible measurement stops, i.e., the two internal reference points. When said measurement buttons are actuated, a distance measurement is triggered with the reference point associated with the actuated button, and the measured distance value is then displayed in the display on the device.
A hand-held device for distance measurement and coordinate determination using geodetic measurements is made known in DE 31 22 483 A1. In order to create a simple and lightweight hand-held device for short-range measurements, said device comprises, among other things, an adjustable stand capable of being attached to the distance measuring device in a plane that is perpendicular to the direction of measurement. The height-adjustable stand made known in DE 32 22 483 A1 has a double function. On the one hand, it ensures that the measuring device can be held in the hand without shaking and, on the other hand, it ensures that the distance measuring device is centered on a reference point on the ground. The disclosed distance measuring device must be placed along with its stand in the zero point (reference point) of the path to be measured.
In the case of an advantageous configuration of the device made known in DE 31 22 483 A1, the stand is detachably connected to the distance measuring device and also comprises a level vial with bushing to control its perpendicular position.
An auxiliary housing for holding a normally hand-held distance measuring device is made known in DE 198 09 683 A1. Said auxiliary housing is configured as a hollow body and comprises a receptacle for insertion of a distance measuring device. The auxiliary housing is equipped with a threaded bushing for mounting the housing part on a tripod. The longitudinal axis of the threaded bushing for the tripod holder coincides with an abutment surface of the distance measuring device operating as a reference plane when said device is properly inserted in the auxiliary housing. In this manner, the reference point for a distance measurement with the aid of the tripod is equal to the reference point of the hand-held distance measuring device. It is not necessary for the user to change the reference points.
In the case of the distance measuring device disclosed in DE 198 09 683 A1 as well, the user must make certain that the internal reference plane coincides with the zero point of the path he is measuring. Furthermore, in the case of DE 198 09 683A1, if a measuring device is not inserted completely into the holder, the length measurement is faulty, because the measured path started at an incorrect zero point (reference point).